Nickel sulphide ores are presently treated in commercial applications in a variety of processes in which the first step normally is physical concentration by means of flotation to upgrade the nickel content, typically from an initial range of between 0.5% and 2.0% to a concentrated range of between 7 and 25% nickel. This concentrate is then subsequently treated by pyrometallurgical (smelting) methods to produce a nickel matte or an artificial high grade sulphite product containing about 20% to 75% nickel. The matte is then subjected to hydrometallurgical treatment to produce a nickel product.
This combination of pyrometallurgical and hydrometallurgical processing of nickel concentrates is well established commercially with a number of variations, particularly in the hydrometallurgical part. Most processes recover some portion of the associated metal values where present, such as copper and cobalt. In addition, a leach residue containing precious metals, such as gold and silver, as well as platinum group elements, e.g. platinum and palladium, is often produced for subsequent recovery of contained values.
The hydrometallurgical steps for treating nickel matte vary considerably but all known commercial processes have one or more of the following disadvantages:
(i) High costs of reagents such as caustic soda or ammonia, required for neutralization. PA1 (ii) Large byproduct production, such as ammonium sulphate or sodium sulphate, which are difficult to market. PA1 (iii) High energy costs due to large temperature changes during the process. PA1 (iv) Complex and costly process flowsheet, leading to high capital and operating costs.
As an alternative to the established pyrometallurgical/hydrometallurgical route referred to above, there is one known process using wholly hydrometallurgical steps that treats concentrates without smelting. It comprises a pressure leaching stage with ammoniacal solution. This avoids most of the disadvantages associated with the smelting processes, but still suffers from all of the listed disadvantages of the known hydrometallurgical routes, and in fact, is not even as efficient overall as the best of the pyrometallurgical/hydrometallurgical routes.
The present invention provides a process for the hydrometallurgical extraction of copper, nickel and cobalt as well as other metals from sulphide ores. It also provides a process for the hydrometallurgical extraction of nickel and cobalt from laterite ores.
Existing hydrometallurgical processes for laterites also suffer from the above disadvantages, in particular, poor or costly recovery of cobalt. It is accordingly a further object of the invention to provide a process resulting in high recovery of cobalt and nickel at a low cost from liquors resulting from the acid leaching of laterites.